Menu Close

Pain and Temperature

(Sample Lesson)


The sensory pathways that deliver pain and temperature information to the brain are each composed of a receptor and three successive neurons.

A receptor is the initial portion of the first neuron in a pathway, which is sensitive to changes in the environment (= stimuli). Pain receptors (nociceptors) and temperature receptors (thermoreceptors) are unencapsulated and branched, like the fine roots of a plant. Because nociceptors and thermoreceptors contain no specialized structures, they are often referred to as free nerve endings. They are especially abundant in the skin but occur elsewhere in the body. Internal nociceptors are found in a variety of organs, such as the muscles, the joints, the bladder, the gut, and the digestive tract.

Neurons and Pathway

The first neuron in a pain or temperature pathway is called a sensory neuron (or first order neuron). An axon of a sensory neuron passes through the dorsal root ganglion and extends to the dorsal horn of the spinal cord, where it synapses with a second order neuron (or interneuron). The term interneuron applies to any neuron that is located entirely within the central nervous system.

First and second order neurons - labeled

Labeled and Unlabeled Versions
(1125px X 800px)

The axon from the second order neuron decussates (crosses) within the spinal cord and ascends in the spinothalamic tract, along with other second order neurons.

Spinothalamic tract - labeled

Labeled and Unlabeled Versions
(1125px X 1000px)

The spinothalamic tract axons pass through the medulla oblongata region of the brain before terminating at the ventral posterolateral (VPL) nucleus of the thalamus.

Full pain and temperature pathway - labeled

Labeled and Unlabeled Versions
(1125px X 1500px)

In the thalamus, the second order neuron synapses with a third order neuron (interneuron). The axon of the third order neuron then carries signals to the primary somatosensory region of the cerebral cortex, where the input is imaged and interpreted.

Page Attributions

OpenStax, Anatomy and Physiology

Access for free at

Reference: “Cardiac Muscle and Electrical Activity

Wikipedia, the free encyclopedia.

Reference : “Cardiac muscle